r_env_vars

Environment variables to set when calling R

Devtools sets a number of environmental variables to ensure consistent
between the current R session and the new session, and to ensure that
everything behaves the same across systems. It also suppresses a common
warning on windows, and sets NOT_CRAN so you can tell that your
code is not running on CRAN. If NOT_CRAN has been set externally, it
is not overwritten.